Field of the Invention
The present invention relates to a ceramic color composition and a process for producing a sheet glass by using the ceramic color composition.
Heretofore, a so-called ceramic color paste for automobiles has been commonly used, whereby a ceramic color composition is formulated into a paste and screen-printed along the peripheral portion or the center portion of a window glass of an automobile, followed by drying and baking during the bending step. This ceramic color paste is used for the purpose of forming a colored opaque layer by baking it along the peripheral portion of a blank sheet glass and thereby to prevent the deterioration of an urethane adhesive by ultraviolet rays, or to prevent the bonded portion from being seen through from outside the vehicle. As such a composition, a composition prepared by incorporating a heat resistant colored pigment to a glass powder, is known and usually has a color of black or dark gray.
On the other hand, especially in the case of a vehicle rear window glass, a silver paste is printed and baked in a pattern of lines as an electric heater to prevent fogging of the rear window glass. The electrode-forming portion (i.e. the busbar portion) may sometimes be overlapped positionwise with the baking portion of the above-mentioned ceramic color. In such a case, it is usual that a ceramic color paste and a silver paste are lap-printed on a sheet glass, followed by baking.
However, with sheet glass produced by a conventional method, it was inevitable that silver in the silver paste migrated through the ceramic color layer to reach the sheet glass and thereby to develop an amber color. Such color development makes the presence of the electrode portion of the above silver paste distinct, and thus creates a problem that the appearance of the vehicle window glass as observed from outside is thereby substantially impaired.